A phase I dose-escalation study of the polyamine analog PG-11047 in patients with advanced solid tumors

Synthesis and evaluation of a 68Ga-labeled spermine derivative for tumor PET imaging

BACKGROUND

The polyamine transporter system (PTS), which renders it a promising target for tumor therapy and imaging applications, facilitates the transmembrane transport of polyamines. We reported a novel derivative of spermine labeled with gallium-68 ([68Ga]Ga-NOTA-Spermine) for the imaging of the PTS in mouse models of tumor.

RESULTS

The radiochemical yield of [68Ga]Ga-NOTA-Spermine was determined to be 64-69 %, demonstrating exceptional stability and radiochemical purity (>98 %). Cellular uptake experiments revealed that A549 cells exhibited peak uptake of [68Ga]Ga-NOTA-Spermine at 90 min (15.4 % ± 0.68 %). Biodistribution analysis demonstrated significant accumulation of [68Ga]Ga-NOTA-Spermine in kidneys and liver, while exhibiting low uptake levels in muscle, brain, and bones. Furthermore, Micro-PET/CT scans conducted on A549 tumor-bearing mouse models indicated substantial uptake of [68Ga]Ga-NOTA-Spermine, with maximum tumor/muscle (T/M) ratios reaching 3.71.

CONCLUSION

These results suggest that [68Ga]Ga-NOTA-Spermine holds potential as a PET imaging agent for tumors with high levels of PTS.

The Polyamine Analogue Ivospemin Increases Chemotherapeutic Efficacy in Murine Ovarian Cancer

Polyamines are small polycationic alkylamines that are absolutely required for the continual growth and proliferation of cancer cells. The polyamine analogue ivospemin, also known as SBP-101, has shown efficacy in slowing pancreatic and ovarian tumor progression in vitro and in vivo and has demonstrated encouraging results in early pancreatic cancer clinical trials. We sought to determine if ivospemin was a viable treatment option for the under-served platinum-resistant ovarian cancer patient population by testing its efficacy in combination with commonly used chemotherapeutics. We treated four ovarian adenocarcinoma cell lines in vitro and found that each was sensitive to ivospemin regardless of cisplatin sensitivity. Next, we treated patients with ivospemin in combination with four commonly used chemotherapeutics and found that ivospemin increased the toxicity of each; however, only gemcitabine and topotecan combination treatments were more effective than ivospemin alone. Using the VDID8+ murine ovarian cancer model, we found that the addition of ivospemin to either topotecan or gemcitabine increased median survival over untreated animals alone, delayed tumor progression, and decreased the overall tumor burden. Our results indicate that the combination of ivospemin and chemotherapy is a worthwhile treatment option to further explore clinically in ovarian cancer.

Polyamine Signal through HCC Microenvironment: A Key Regulator of Mitochondrial Preservation and Turnover in TAMs

Hepatocellular carcinoma (HCC) is the most common primary liver cancer, and, with increasing research on the tumor immune microenvironment (TIME), the immunosuppressive micro-environment of HCC hampers further application of immunotherapy, even though immunotherapy can provide survival benefits to patients with advanced liver cancer. Current studies suggest that polyamine metabolism is not only a key metabolic pathway for the formation of immunosuppressive phenotypes in tumor-associated macrophages (TAMs), but it is also profoundly involved in mitochondrial quality control signaling and the energy metabolism regulation process, so it is particularly important to further investigate the role of polyamine metabolism in the tumor microenvironment (TME). In this review, by summarizing the current research progress of key enzymes and substrates of the polyamine metabolic pathway in regulating TAMs and T cells, we propose that polyamine biosynthesis can intervene in the process of mitochondrial energy metabolism by affecting mitochondrial autophagy, which, in turn, regulates macrophage polarization and T cell differentiation. Polyamine metabolism may be a key target for the interactive dialog between HCC cells and immune cells such as TAMs, so interfering with polyamine metabolism may become an important entry point to break intercellular communication, providing new research space for developing polyamine metabolism-based therapy for HCC.

Polyamine-Based Nanostructures Share Polyamine Transport Mechanisms with Native Polyamines and Their Analogues: Significance for Polyamine-Targeted Therapy

Polyamines are small polycationic alkylamines involved in many fundamental cellular processes, including cell proliferation, survival, and protection from oxidative stress. Polyamine homeostasis is tightly regulated through coordinated biosynthesis, catabolism, and transport. Due to their continual proliferation, cancer cells maintain elevated intracellular polyamine pools. Both polyamine metabolism and transport are commonly dysregulated in cancer, and as such, polyamine analogues are a promising strategy for exploiting the increased polyamine requirement of cancer cells. One potential polyamine analogue resistance mechanism is the downregulation of the poorly defined polyamine transport system. Recent advances in nanomedicine have produced nanostructures with polyamine analogue-based backbones (nanopolyamines). Similar nanostructures with non-polyamine backbones have been shown to be transported by endocytosis. As these polyamine-based nanoparticles could be a method for polyamine analogue delivery that bypasses polyamine transport, we designed the current studies to determine the efficacy of polyamine-based nanoparticles in cells lacking intact polyamine transport. Utilizing polyamine transport-deficient derivatives of lung adenocarcinoma lines, we demonstrated that cells unable to transport natural polyamines were also resistant to nanopolyamine-induced cytotoxicity. This resistance was a result of transport-deficient cells being incapable of importing and accumulating nanopolyamines. Pharmacological modulation of polyamine transport confirmed these results in polyamine transport competent cells. These studies provide additional insight into the polyamine transport pathway and suggest that receptor-mediated endocytosis is a likely mechanism of transport for higher-order polyamines, polyamine analogues and the nanopolyamines.

Polyamines in cancer: integrating organismal metabolism and antitumour immunity

The natural mammalian polyamines putrescine, spermidine and spermine are essential for both normal and neoplastic cell function and replication. Dysregulation of metabolism of polyamines and their requirements is common in many cancers. Both clinical and experimental depletion of polyamines have demonstrated their metabolism to be a rational target for therapy; however, the mechanisms through which polyamines can establish a tumour-permissive microenvironment are only now emerging. Recent data indicate that polyamines can play a major role in regulating the antitumour immune response, thus likely contributing to the existence of immunologically 'cold' tumours that do not respond to immune checkpoint blockade. Additionally, the interplay between the microbiota and associated tissues creates a tumour microenvironment in which polyamine metabolism, content and function can all be dramatically altered on the basis of microbiota composition, dietary polyamine availability and tissue response to its surrounding microenvironment. The goal of this Perspective is to introduce the reader to the many ways in which polyamines, polyamine metabolism, the microbiota and the diet interconnect to establish a tumour microenvironment that facilitates the initiation and progression of cancer. It also details ways in which polyamine metabolism and function can be successfully targeted for therapeutic benefit, including specifically enhancing the antitumour immune response.

Expanded Potential of the Polyamine Analogue SBP-101 (Diethyl Dihydroxyhomospermine) as a Modulator of Polyamine Metabolism and Cancer Therapeutic

Naturally occurring polyamines are absolutely required for cellular growth and proliferation. Many neoplastic cells are reliant on elevated polyamine levels and maintain these levels through dysregulated polyamine metabolism. The modulation of polyamine metabolism is thus a promising avenue for cancer therapeutics and has been attempted with numerous molecules, including enzyme inhibitors and polyamine analogues. SBP-101 (diethyl dihydroxyhomospermine) is a spermine analogue that has shown efficacy in slowing pancreatic tumor progression both in vitro and in vivo; however, the mechanisms underlying these effects remain unclear. We determined the effects of the SBP-101 treatment on a variety of cancer cell types in vitro, including lung, pancreatic, and ovarian. We evaluated the activity of enzymes involved in polyamine metabolism and the effect on intracellular polyamine pools following the SBP-101 treatment. The SBP-101 treatment produced a modest but variable increase in polyamine catabolism; however, a robust downregulation of the activity of the biosynthetic enzyme, ornithine decarboxylase (ODC), was seen across all of the cell types studied and indicates that SBP-101 likely exerts its effect predominately through the downregulation of ODC, with a minor upregulation of catabolism. Our in vitro work indicated that SBP-101 was most toxic in the tested ovarian cell lines. Therefore, we evaluated the efficacy of SBP-101 as a monotherapy in the immunosuppressive VDID8⁺ murine ovarian model. Mice treated with SBP-101 demonstrated a delay in tumor progression, a decrease in the overall tumor burden, and a marked increase in median survival.

The Association between Spermidine/Spermine N1-Acetyltransferase (SSAT) and Human Malignancies

Spermidine/spermine N¹-acetyltransferase (SSAT) functions as a critical enzyme in maintaining the homeostasis of polyamines, including spermine, spermidine, and putrescine, in mammalian cells. SSAT is a catalytic enzyme that indirectly regulates cellular physiologies and pathways through interaction with endogenous and exogenous polyamines. Normally, SSAT exhibits only at a low cellular level, but upon tumorigenesis, the expression, protein level, and activities of SSAT are altered. The alterations induce cellular damages, including oxidative stress, cell cycle arrest, DNA dynamics, and proliferation by influencing cellular mechanisms and signaling pathways. The expression of SSAT has been reported in various studies to be altered in different cancers, and it has been correlated with tumor development and progression. Tumor grades and stages are associated with the expression levels of SSAT. SSAT can be utilized as a target for substrate binding, and excreted metabolites may be used as a novel cancer biomarker. There is also potential for SSAT to be developed as a therapeutic target. Polyamine analogs could increase SSAT expression and increase the cytotoxicity of chemotherapy to tumor cells. Drugs targeting polyamines and SSAT expression have the potential to be developed into new cancer treatments in the future.

Metabolism and function of polyamines in cancer progression

Polyamines are essential for the proliferation, differentiation, and development of eukaryotes. They include spermine, spermidine, and the diamine precursor putrescine, and are low-molecular-weight, organic polycations with more than two amino groups. Their intracellular concentrations are strictly maintained within a specific physiological range through several regulatory mechanisms in normal cells. In contrast, polyamine metabolism is dysregulated in many neoplastic states, including cancer. In various types of cancer, polyamine levels are elevated, and crosstalk occurs between polyamine metabolism and oncogenic pathways, such as mTOR and RAS pathways. Thus, polyamines might have potential as therapeutic targets in the prevention and treatment of cancer. The molecular mechanisms linking polyamine metabolism to carcinogenesis must be unraveled to develop novel inhibitors of polyamine metabolism. This overview describes the nature of polyamines, their association with carcinogenesis, the development of polyamine inhibitors and their potential, and the findings of clinical trials.

A Phase Ib multicenter, dose-escalation study of the polyamine analogue PG-11047 in combination with gemcitabine, docetaxel, bevacizumab, erlotinib, cisplatin, 5-fluorouracil, or sunitinib in patients with advanced solid tumors or lymphoma

PURPOSE

Polyamines are absolutely essential for maintaining tumor cell proliferation. PG-11047, a polyamine analogue, is a nonfunctional competitor of the natural polyamine spermine that has demonstrated anticancer activity in cells and animal models of multiple cancer types. Preclinical investigations into the effects of common chemotherapeutic agents have revealed overlap with components of the polyamine metabolic pathway also affected by PG-11047. This report describes a Phase Ib clinical trial investigating PG-11047 in combination with cytotoxic and anti-angiogenic chemotherapeutic agents in patients with advanced refractory metastatic solid tumors or lymphoma.

METHODS

A total of 172 patients were assigned to treatment arms based on cancer type to receive the appropriate standard-of-care therapy (gemcitabine, docetaxel, bevacizumab, erlotinib, cisplatin, 5-fluorouracil (5-FU), or sunitinib as directed) along with once weekly intravenous infusions of PG-11047. PG-11047 dose escalation ranged from 50 to 590 mg.

RESULTS

The maximum tolerated dose (MTD) of PG-11047 in combination with bevacizumab, erlotinib, cisplatin, and 5-FU was 590 mg. Dose-limiting toxicities (DLTs) in these groups were rare (5 of 148 patients). Overall partial responses (PR) were observed in 12% of patients treated with PG-11047 and bevacizumab, with stable disease documented in an additional 40%. Stable disease occurred in 71.4% of patients in the 5-FU arm, 54.1% in the cisplatin arm, and 33.3% in the erlotinib arm. Four of the patients receiving cisplatin + PG-11047 (20%) had unconfirmed PRs. MTDs for gemcitabine, docetaxel, and sunitinib could not be determined due to DLTs at low doses of PG-11047 and small sample size.

CONCLUSIONS

Results of this Phase Ib trial indicate that PG-11047 can be safely administered to patients in combination with bevacizumab, erlotinib, cisplatin, and 5-FU on the once weekly dosing schedule described and may provide therapeutic benefit. The manageable toxicity profile and high MTD determination provide a safety profile for further clinical studies.